1. Field of the Invention
This invention relates generally to gas generators such as are used, for example, in the propulsion and/or guidance of guided missiles. More specifically, the invention relates to a fuel supply system for a gas generator.
2. Description of the Prior Art
A gas generator normally comprises a combustion chamber and a fuel reservoir, fuel being supplied to the combustion chamber and burned therein to produce a hot gas which is supplied to a load such as an outlet choke. The fuel may be a monopropellant or a bipropellant but in each case it has to be supplied to the combustion chamber, normally under pressure, and there are in existence a number of different fuel supply or pressurisation systems. The fuel reservoir may be pressurized using a gas bottle controlled by valve means or using a solid charge igniter, such as cordite breech igniter, connected to the fuel reservoir by pressure control means and having some form of igniter associated therewith, the charge producing a pressurised gas which in turn pressurises the fuel reservoir.
An alternative known fuel supply system relies on a pump to transfer fuel from the reservoir to the combustion chamber and the pump may be energised from a power supply (local or remote) or by a turbine driven by an auxiliary gas generator. A further alternative system is of the so-called bootstrap type in which gas generated in the combustion chamber is used to pressurise the fuel reservoir through pressure-amplifying means, such as a differential piston. All of these known fuel pressurising/supply systems suffer from either or both of the disadvantages of increasing the mass of the gas generator and involving moving parts which are particularly serious in the context of guided missiles because space is always at a premium and components having moving parts give rise to problems of reliability.
One of the most convenient fuel-pressurisation systems is that employing a gas bottle as described above but apart from possessing the disadvantage of occupying a relatively large space, the gas bottle gives rise to grave handling problems. For a typical gas generator, the pressure required to be stored in the gas bottle is of the order of 6000 p.s.i. and any container pressurised to this level is potentially dangerous and the safety procedure for handling can be onerous.
The sequence of events in a combustion chamber can be summarised as follows:
fuel injection PA1 fuel atomisation PA1 fuel vapourisation PA1 chemical reaction producing hot gasses. PA1 Chugging--a low frequency oscillation in the range 20 to 200 Hz due to pressure interactions between the fuel and combustion chamber. PA1 Buzzing--usually due to vibration of the gas generator in the range of 200 to 2000 Hz. PA1 Screaming--this occurs at a frequency above 1000 Hz and is due to combustion pressure waves and can be destructive.
The time taken for the chemical reaction to take place following the fuel injection varies with the type of fuel used and the conditions but is often of the order of several milliseconds. In the steady state condition, the process is continuous but in the presence of perturbations, oscillations in the pressure of the generated gas can occur and are classified as follows:
It will be appreciated that due to the process time delay between fuel injection and chemical reaction, it is possible to generate pressures in the combustion chamber which are higher than the fuel injection pressure. To date, this phenomenon has been considered undesirable bu the present invention turns on the concept of generating these higher pressures in the combustion chamber and harnessing them for fuel pressurisation.